So N N, Wong P C, Ko R C
Department of Biochemistry, Faculty of Medicine, University of Hong Kong.
Int J Parasitol. 1992 Jul;22(4):427-33. doi: 10.1016/0020-7519(92)90143-9.
Gravid Angiostrongylus cantonensis can utilize radiolabelled bicarbonate, orotate, uracil, uridine and cytidine but not cytosine, thymine and thymidine for the synthesis of RNA and DNA. In cell-free extracts of the worm, a phosphoribosyltransferase was shown to convert orotate to OMP and uracil to UMP. A similar reaction was not observed with cytosine and thymine. Uridine was readily phosphorylated by a kinase but a similar reaction for thymidine and deoxyuridine was not found. Cytidine could be phosphorylated by a kinase or be deaminated by a deaminase to uridine. No deaminase for cytosine was detected. There was also no phosphotransferase activity for pyrimidine nucleosides in the cytosolic or membrane fractions. Pyrimidine nucleosides were, in general, converted to the bases by a phosphorylase reaction but only uracil and thymine could form nucleosides in the reverse reaction. The activity of thymidylate synthetase was also measured. These results indicate that the nematode synthesizes pyrimidine nucleotides by de novo synthesis and by utilization of uridine and uracil and that cytosine and thymine nucleotides are formed mainly through UMP. The thymidylate synthetase reaction appears to be vital for the growth of the parasite.
妊娠广州管圆线虫可利用放射性标记的碳酸氢盐、乳清酸、尿嘧啶、尿苷和胞苷来合成RNA和DNA，但不能利用胞嘧啶、胸腺嘧啶和胸苷。在该线虫的无细胞提取物中，一种磷酸核糖基转移酶可将乳清酸转化为乳清酸核苷酸（OMP），将尿嘧啶转化为尿苷酸（UMP）。胞嘧啶和胸腺嘧啶未观察到类似反应。尿苷可被一种激酶轻易磷酸化，但未发现胸腺嘧啶核苷和脱氧尿苷有类似反应。胞苷可被一种激酶磷酸化或被一种脱氨酶脱氨生成尿苷。未检测到胞嘧啶脱氨酶。胞质或膜部分中嘧啶核苷也不存在磷酸转移酶活性。一般来说，嘧啶核苷通过磷酸化酶反应转化为碱基，但只有尿嘧啶和胸腺嘧啶能在逆反应中形成核苷。还测定了胸苷酸合成酶的活性。这些结果表明，该线虫通过从头合成以及利用尿苷和尿嘧啶来合成嘧啶核苷酸，胞嘧啶和胸腺嘧啶核苷酸主要通过UMP形成。胸苷酸合成酶反应似乎对该寄生虫的生长至关重要。
